An E-bird with attitude!
Bank" .mov clip
(right click and save to drive - 7.5 megs)
and "Sparky" Paul's inverted V tail camera plane for its aesthetics:
I set out to design the perfect foamy E-trainer.
I felt I had already achieved the "virtually indestructible" goal in my prior "Wally Wing" project. It utilizes a knock-off power pod and taped foam wings from a $4 hand chuck Wal-Mart glider:
It has endured full speed contact with a goal post and only sustained a minor dent in the LE. Even power dives into the ground have never ended a day of flying.
I elected to borrow the same simple and low cost construction techniques but have rudder and elevator control for Polly. More accurately, ruddervators, using two mixed HS-81's in the wing.
My first attempt had too much dihedral and not enough tail moment resulting in anything but tame behavior. Exciting flying fun to be sure, but she was no trainer. The spruce stick booms left a lot to be desired in the strength department as well.
After much trial and error, I ended with a layout which has longer booms of carbon fiber tubing and less dihedral in the wings. I also choose higher aspect ratio tail feathers. Adding some sweep to the wing tip sections helped with the ever-increasing nose length needed to achieve the proper CG without adding redundant nose weight.
The stock glider's foam wings are cut up and reglued to shape with 5 minute epoxy after adding a 1/8 by 1/2 inch spruce spar cut in the bottom vertically at the quarter chord sweep line. Thin ply doublers are added on each side of the spar at the breaks. A 1.5 inch wide balsa trailing edge is added and some reinforced strapping tape is applied on the LE and root for dent resistance. Colored packing tape finishes it off.
The redesigned power pod allows a larger selection of 8 cell battery packs ranging from 1600 NiMH's to 1400AE NiCad's. A stock Cermark S-400 6vt motor with a Kontronik Rondo 400 speed control installed turns a Graupner CAM 6.3 x 3 folder set up as a pusher.
Constructed from the stock nose of the "dime-store" glider's fuselage, the pod is reinforced with sidewalls of corrugated plastic sign material (Coroplast/Corex) that double as motor mounts. Two bamboo skewers and nylon wire ties are all that's needed to secure it snuggly in place. An additional piece of this plastic is attached with strapping tape under the motor enclosing the remaining open area. This piece adds structural strength where the wing attaches as well.
A hatch is cut out of the front top for easy battery exchanges and is simply Velcroed in place. The small gap under this "canopy" from the raised Velcro allows cooling air to flow over the tops of the batteries and out the back past the motor. The pod is held onto the wing with conventional rubber bands over pegs in the front with the rear posts there just to restrain the bands from slipping off the back.
The foam wrapped Hitec 555 receiver fits securely behind the power pack completing the package. A detachable antenna wire using a single servo connector stays with the wing and tail for easy pod removal.
The tail is simply a single piece cut from Coroplast that has a web removed to create the hinge line. Small straws are taped over the LE and the TE is sliced and taped flat for streamlining. It is firmly attached to the twin CF booms with nylon cable clamps and bolts.
The booms attach to the wing in the same manner with one nylon bolt through a thin-ply reinforced hole in the TE and another into a threaded spacer glued into the wing against the spar.
Flexible control rods from the flush bottom mounted wing servos run along the booms and attach to the control horns on the top of the tail for positive tension during pitch-up loads.
The airfoil from the modified "Sky Rider" foam wing appears to be similar to a 12 percent thick S3021 section.
This wing continues to impress me with its great glide ratio. Even with a 10.5 to 11.5 ounce per square foot wing loading, a power off toss can get Polly far enough out that you really dread the walk to retrieve her. In fact, since I had the CG worked out from the first prototype, when I test glided her with all the final modifications completed, I knew from the first 10 feet of glide she was trimmed correctly. To save me the walk, I just hit the juice and never looked back.
Continuous banked thermaling turns are very relaxing and are surprisingly tight for her wing loading. With good throttle management I routinely achieve 20 to 30 minute flights from various 8-packs. The only complaint I can find in her flight characteristics, and it's a minor one, is her roll response coming out of very steep banked turns. There is noticeable yaw and lag time prior to the roll. I may just be expecting too much from an RE plane at that attitude, but this trait might be helped with some further vertical stab and rudder sizing.
All in all I'm very happy with her current feel. She's very comfortable to fly and holds a turn securely with just gentle back pressure without any wobble or Dutch roll effects.
Common RE stunts can be flown from level flight such as loops, stall turns, hammerheads, wingovers, etc., and even some inverted. Personally, I'm having trouble with decent rolls, but I never could roll an RE ship. Best I get is a twisted loop! Climb is very respectable at full throttle but might even be spectacular with a gearbox. Although appearing that she might be somewhat draggy, power off hi-speed flybys are surprisingly silent leading me to believe she's pretty darn clean.
I'm constantly amazed at the speed range of this wing. On 1/3 throttle you can hang on the bleeding edge with good cues that you're nearing her limits. With the correct CG, stalls are straight-ahead and mild with very quick recovery even if you start to drop a wing. About the hardest aspect of flying Polly is judging landings due to that extra long glide on final. Reminds me of my old two-meter glider days.
Survivability has been tested with everything from a power dive in from 50 feet (don't ask) to botched down-wind cart wheeled "landings". No real damage from anything except for broken rubber bands, a wrinkled nose (mine and Polly's), relocated motor, and a popped nylon boom bolt. With the advantages of such simple crash-proof construction does come the price of some added preflight responsibility however. Although it takes only seconds, the tail and wing need to be eyeballed for alignment, and the pod position checked for correct CG location before each flight. All in all, a small price to pay I'd say.
Polly gets flown lots as what you might call a power assisted HLG. It's a real challenge poking around low looking for a "hit", cutting power and winding her up. If I get spit out, I can just power away to search for another source, or climb back up to recatch the same one that kicked me out! Cheating? I guess, but who cares? I'm having hours of great flying fun on just a few pre-charged packs and most of it is close and in my face!
Even so, I'll still have to rate this bird an outfield flyer, since she likes to move pretty quickly if you let her.
Is she the perfect E-trainer? Well I won't go that far but I will say that she's rekindled my affection with the relaxed flying style that rudder/elevator designs make possible. With her effortless soaring ability and forgiving nature she's a real pleasure to fly. Maybe she's that one plane that can do many things well?
Being a tough foamy pusher, this bird gives me a renewed confidence to brave flying low, slow, and close in without worrying about racking her up. With her good performance and speed range, she makes a fine duration power player as well. Add the fact that Polly was built for less than $15 minus electrics in only a few easy evenings, and she's a winner in my book!
Take a Polly tail and add it to a Wally Wing.....A convertable sportster? Also possible aileron trainer.
(c) 2001, 2007 Ken Hill - Ace Sim RC - Medford Oregon